The results explain why we need to "create more flexibility in our society."

The 9-to-5 workday originated with American labor unions in the 1800s, and today, the eight-hour workday is the norm. But however normalized the schedule, it is directly opposed to something more powerful: biology.

In a new study, scientists report that people whose internal body clocks tell them to go to bed late, but are then forced to wake up early, have a lower resting brain connectivity in the regions of the brain linked to consciousness.

Scientists shared their findings Friday in the journal SLEEP, with the article, “Circadian phenotype impacts the brain’s resting state functional connectivity, attentional performance and sleepiness.”

Lead author and University of Birmingham researcher Elise Facer-Childs, Ph.D., explains to Inverse that while varying levels of brain connectivity do not always relate to something negative, in this study, lower levels were less than positive.

During the experiment, the scientists evaluated the brain function of 38 people while they slept, measuring their levels of melatonin and cortisol with MRI scans. They were also asked to report on their levels of sleepiness and when during the day they felt most alert.

"Night owls" are less compatible with the 9-to-5 work week.

Ultimately, they found that “morning larks” had higher resting brain connectivity — which in turn was associated with better attentional performance and lower daytime sleepiness over the course of the working day. Facer-Childs explains that this likely means their brains were more primed for doing tasks and being less sleepy.

Why some people are primed to wake up early and others are driven to go to bed late stems from their genes. A study published in January in Nature Communications found that genes can even shift a person’s natural waking time by up to 25 minutes.

The two hormones involved in the sleep and wake cycle have a role as well: Melatonin and cortisol levels differ significantly between the two groups of people over the course of a 24-hour period. These hormones peak for “night owls” about three to four hours after “morning larks.”

“We all know that some of us are better in the morning and some of us love burning that midnight oil, but people don’t tend to think about why and how,” Facer-Childs explains. “Our research is looking at an area of science that is so relevant to every single one of us, which makes it so accessible.

“I believe that accounting for individual differences in sleep patterns and body clocks could open up a relatively untapped source, could contribute to being at our best, both mentally and physically.”

"Morning larks" have more brain connectivity.

This research also hints that “night owls” are less compatible to the 9-to-5 work day than people who naturally wake up earlier. It’s theorized that lower levels of brain connectivity cause “night owls” to have poorer attention, slower reactions, and increased sleepiness throughout the hours of a typical work day. Facer-Childs believes this study and others suggest that the rigid 9-to-5 schedule might need to change.

“I believe that the abundance of research coming out now that links misalignment and sleep disruption to negative health and performance supports the need to create more flexibility in our society,” Facer-Childs says.

“I realize that there is a need for some sort of constrained routine, but being able to take these individual differences into account and allow people a few hours of flexibility could have a considerable impact.”

Partial Abstract:

INTRODUCTION: Functional connectivity (FC) of the human brain’s intrinsically connected networks underpins cognitive functioning and disruptions of FC are associated with sleep and neurological disorders. However, there is limited research on the impact of circadian phenotype and time of day on FC.

STUDY OBJECTIVES: The aim of this study was to investigate resting state FC of the default mode network (DMN) in Early and Late circadian phenotypes over a socially constrained day.

METHODS: 38 healthy individuals (14 male, 22.7 ± 4.2 years) categorized as Early (n =16) or Late (n =22) using the Munich ChronoType Questionnaire took part. Following a two week baseline of 35 actigraphy coupled with saliva samples for melatonin and cortisol rhythms, participants underwent testing at 14.00 h, 20.00 h, and 08.00 h the following morning. Testing consisted of resting-state functional MRI, a structural T1 scan, attentional cognitive performance tasks, and self-reported daytime sleepiness. Seed-based FC analysis from the medial prefrontal and posterior cingulate cortices of the DMN was performed, compared between groups and linked with behavioral data.